1. Technical Field of the Invention
The present invention relates generally to a fuel injector designed to inject fuel into an internal combustion engine in an unique spray pattern, and more particularly to an improved structure of such a fuel injector designed to optimize the pattern of a spray of fuel when hitting a head of an intake valve of the engine.
2. Background Art
Japanese Patent Publication Nos. 6-101603 and 4-121435 disclose an injector orientation changing mechanism which is installed in an intake manifold of an internal combustion engine to change the direction in which fuel is sprayed from a fuel injector to an intake port based on operating conditions of the engine in order to optimize the pattern of the sprayed fuel.
Use of such a type of injector orientation changing mechanism results in an increase in production costs of fuel injectors and also requires a complex controller to monitor the operating conditions of the engine to control the movement of the injector orientation changing mechanism. The injector orientation changing mechanism is, therefore, unsuitable for practical use or purposes.
In recent years, there has been proposed a fuel injection system, as discussed in the 8th Aachen Colloquium, which works to orient a jet of fuel to a bottom wall surface of an intake port of the engine (i.e., an upstream portion of the head of an intake valve) for the purpose of reducing HC emissions at start and right after start of the engine. The system is designed based on the fact that when a large amount of fuel sticks to around an exhaust port of a combustion chamber of the engine, it will cause most of the fuel to be discharged from the exhaust port without being burned, thus resulting in an increased amount of HC emissions. Specifically, an fuel injection valve is so installed as to produce and direct a spray of fuel to the bottom wall surface of the intake port to wet it with much fuel for minimizing adhesion of fuel to around the exhaust port.
However, experimental researches made by the inventors of this application have showed that when a large amount of fuel is, like the system, as described above, sprayed and adhered to the bottom wall surface of the intake port of the engine to wet it at the start of the engine when the fuel injection valve is required to spray much fuel, it will cause the fuel staying on the bottom wall surface the intake port to be vaporized in an instant and drawn into the combustion chamber, so that an air-fuel mixture in the combustion chamber is enriched undesirably, thus resulting in rich misfire leading to an increased amount of HC emissions from the engine.
The fuel injection timing is usually controlled in two modes: an intake synchronous injection mode in which cylinders of the engine are identified using an output of a cam sensor or a crank sensor, and the fuel is jetted into each cylinder in synchronization with the intake stroke of a piston thereof (i.e., during opening of intake valves) and an intake asynchronous injection mode in which the fuel is jetted into the cylinder during closing of the intake valves regardless of the stroke of the piston. Usually, at the start of the engine, the intake asynchronous injection mode is entered until the cylinders are identified. After such identification, the intake synchronous injection mode is subsequently entered. Specifically, the fuel injection timing is switched between the synchronous injection mode and the intake asynchronous injection mode based on running conditions of the engine.
In the intake asynchronous injection mode, the intake ports of the combustion chamber of the engine are kept closed, so that no air flows exist in the intake ports, thus causing a spray of fuel to go straight to a target spot. In the intake asynchronous injection mode, air flows are produced in the intake ports, thus causing a stream of spray of fuel to be based or shifted undesirably by the air flow in each of the intake ports toward exhaust valve of the engine.
Therefore, when a target area to which the fuel injector aims at spraying fuel is selected toward the center of the head of the intake valve in the intake asynchronous injection mode in order to minimize wetting of the bottom wall surface of the intake port with fuel, it will eliminate the problem of rich misfire, but however, the shifting of the stream of fuel spray arising from the air flow within the intake port in the intake synchronous injection mode results in an increased amount of fuel sticking to around the exhaust port in the combustion chamber. This will lead to an increase in amount of fuel discharged from the exhaust port without being burned, thereby increasing HC emissions from the engine undesirably.